hunting/OWASP-Top-10/A01-Broken-Access-Control/open-redirect/README.md

Open Redirect Vulnerability

Description

Open redirect vulnerabilities occur when a web application accepts user-controllable input that specifies a link to an external site and uses that link in a redirect. This vulnerability can be exploited by attackers to redirect users to malicious websites while making the URL appear legitimate.

Common Vulnerabilities

• Unvalidated redirect parameters (e.g., ?url=, ?redirect=, ?next=)
• Return URL manipulation in authentication flows
• Post-login redirects
• Logout redirects
• URL parameter injection
• Header-based redirects (e.g., Location, Refresh headers)

Impact

• Phishing attacks
• Credential theft
• Malware distribution
• Bypassing security controls (e.g., URL whitelisting)
• Social engineering attacks

Testing Approach

1. Identify redirect parameters in URLs (e.g., url, redirect, next, return, continue)
2. Test with external URLs (e.g., http://evil.com)
3. Try various encoding techniques to bypass filters
4. Test protocol handlers (e.g., javascript:, data:)
5. Test absolute and relative paths
6. Check POST-based redirects in addition to GET parameters

Prevention

• Avoid using user-supplied input for redirects
• Use a mapping of allowed redirect destinations
• Validate redirect URLs against a whitelist
• Use relative URLs where possible
• Implement proper input validation and sanitization